Electricity is present and used almost everywhere in modern life. However, the flow of electrical current exceeding a threshold level through the human body can cause electrical shock. Electrical shock can be hazardous and known adverse consequences of electrical shock on the human body include the causing of ventricular fibrillation, respiratory arrest, nerve damage, asphyxia, and burns. Ventricular fibrillation is known to be a main cause of fatal accidents by electrical shock in mains power supply environment.
A person is able to feel the flow of current when the current flowing through the human body reaches a “perception threshold”. The typical perceptible threshold for an average human body is about 1 mA at the typical mains frequency of 50 Hz or 60 Hz.
When the current flowing through the human body reaches a “let go threshold”, the current flow can cause involuntary muscle contraction or tetany. When this happens, an affected person would not be able to voluntarily control muscles to release grip on a dangerously electrified object and this can result in prolonged contact with the electrified object. A prolonged exposure to a shock current at or around the let-go threshold can cause bodily damage. The typical “let go threshold” for women is between 5 mA and 7 mA and between 7 mA and 10 mA for men. For a person of 68-Kg (150-lb) weight, a typical “let go threshold” current is about 10 mA. The typical “let go threshold” for an average human body at the typical mains frequency is usually taken to be about 10 mA.
When the current flowing through the human body reaches a “ventricular fibrillation threshold”, ventricular fibrillation will occur. The typical ventricular fibrillation threshold or an average human body is about 100 mA at the typical mains frequency. The actual ventricular fibrillation threshold depends on physiological parameters such as anatomy of the body, state of cardiac function, etc. as well as on electrical parameters such as duration and pathway of current flow.
Low frequency alternating current (AC) in the frequency range of between 15-100 Hz, for example at 50 Hz or 60 Hz, is considered to be more dangerous than direct current (DC) or high frequency AC, since the ventricular fibrillation threshold is considerably lower if the current flow is prolonged beyond one cardiac cycle. At these low frequencies, the let-go threshold is relatively low and the shock current can easily exceed the let-go threshold while not delivering enough initial energy to expel the person away from the source.
A current higher than the ventricular fibrillation threshold which passes through a human body can likely cause nerve or tissue damage, burns and death.
Mains power supply (or ‘mains power’ or ‘main supply’ in short) herein means the general-purpose alternating-current (AC) electric power supply which is also known as household power, household electricity, house current, power-line, domestic power, wall power, line power, AC power, city power, street power, grid power, etc. Most mains power in the world either operate at a standard frequency of 50 Hz (Europe) or 60 Hz (US) sinusoid.